Hi,
This is in reply to the three options listed for buying a round knife.
I have no experience of Stolhman knives but I note that they offer s/steel blades and that for me is a real turn off. The only stainless steel I have ever had that took and held an edge was a pocket knife made by Falkniven out of a laminated stainless with a powdered stainless core. But as sharp as it is I am told they are very prone to chipping as it is not a tough steel.
I have several early Osborne knives with stars or "X" or "XX" stamped on the blade. They are all excellent knives. But I have also seen the quality of other Osbourne hand tools decline in recent years and I do not believe the round knives would be exempt from this drop in quality and finish, so I would not buy a #70 round knife.
I would hunt down a round knife with some age on it, through a reputable seller or through ebay.. Makers to look for would include Osborne , Rose, Gomph, Dixon and Collins. With ebay ask direct questions about the knife as I have bought on the basis of the picture only to find the othe side has been in contact with wet card board and was heavilly pitted. All was not lost as the handle was great and I had a nice blade on another osborne with a split handle and an owners initals scratched into it. The only thing that says it is not original is the use of a 1/8 diameter brass pin to compensate for the different hole positions in blade and handle.
If you end up with somthing you are not happy with you can always relist it as what it is. I have sold a heavily pitted knife that I had rust neutralised the blade on, to a lady who wanted the rustic look as she was going to mount it on a board with some other tools to make a "work bench" diarama and set it into the top of a coffee table she was having made. I was honest with her, she got what she wanted and the knife was not going into the trash. A win all around.
All the best.